/Engine/Source/Runtime/MeshDescription/Public/MeshElementArray.h
This is a special type of iterator which returns successive IDs of valid elements, rather than the elements themselves. It is designed to be used with a range-for: for( const FVertexID VertexID : GetVertices().GetElementIDs() )
{
    DoSomethingWith( VertexID );
}
class TElementIDs